This invention relates generally to an electrophotographic printing machine, and more particularly concerns an apparatus for illuminating and scanning an original document being reproduced thereby.
In the process of electrophotographic printing, a photoconductive surface is uniformly charged and exposed to a light image of an original document. Exposure of the charged photoconductive surface records thereon an electrostatic latent image corresponding to the original document. The electrostatic latent image is then rendered visible by depositing toner particles which adhere electrostatically thereto. Subsequently, the toner powder image is transferred to a sheet of support material which may be paper or a plastic material, amongst others. The toner powder image is, then, permanently affixed to the sheet of support material to provide a copy of the original document.
Multi-color electrophotographic printing is substantially the same as the heretofore discussed process. However, rather than forming a total light image of the original document, successive colored filter light images are formed. Each light image is filtered to produce a single color light image which is a partial light image of the original document being reproduced. The foregoing single color light image exposes the charged photoconductive surface recording thereon a single color electrostatic latent image. The single color light image is developed with toner particles of a color complementary to the single color light image. Thereafter, the single color toner powder image is transferred to the sheet of support material. The foregoing process is repeated a plurality of cycles with differently colored light images and the respective complementarily colored toner particles. Each single color toner powder image is transferred to the sheet of support material in superimposed registration with the prior toner powder image to form a composite multilayered powder image. The multi-colored powder image is coalesced and permanently affixed to the sheet of support material.
In the exposure process, a lamp moves across the original document to illuminate successive incremental areas thereof. In this way, a flowing light image of the original document is projected onto the charged portion of the photoconductive surface. Any oscillation or movement of the lamp in a direction other than the desired direction results in distortions of the light image being projected onto the photoconductive surface. This, in turn, degrades the resultant copy formed thereby. Hereinbefore, cables and pulleys were employed in conjunction with a drive motor to move the scan lamps across the original document. One type of system previously employed is described in U.S. Pat. No. 3,062,094 issued to Mayo in 1962. However, the system described therein makes no effort to minimize the jitter of the lamps moving across the original document.
With the advent of multi-color electrophotographic printing, it has become highly desirable to reproduce original documents such that the resultant copy will be pictorial in quality. This requires the utilization of precise controls in the electrophotographic printing machine to reduce errors contributing to degradation of copy quality. One such error source is the jitter of the scan lamps as they traverse the original document being reproduced.
Accordingly, it is a primary object of the present invention to improve the optical system illuminating an original document in an electrophotographic printing machine.